How to protect vbulletin

My freind is running a vbulletim board just like this forums.
last wk his site was hacked and slowed down for 5 hrs and then completely deleted.
What are the security holes in this Board and how to protect
it from future attacks?
Is it better to go for CGI scrpt or PHP scrpt Board?
Any scrpt that could be used to limit the No of posts
that a member is allowed?
Please in detail.

 

 

 

 

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